The present invention relates to producing accelerated aging in light sensitive materials.
Weathering units and fade units are used to generate accelerated aging or fading of light sensitive materials by exposing the light sensitive materials to incident radiation levels above the levels typically found in office or home environments.
Existing units rely on high intensity xenon discharge lamps to create levels of incident radiation that are 2 to 4 times as intense as the radiation from the sun. These systems typically employ lamps that require 6000-12000 watts of electrical power to operate.
Much of the energy given off by such lamps is in the form of heat. To accommodate the heat generated by these lamps, accelerated aging units require large amounts of cooling air to keep the light sensitive materials at ambient temperature. Alternatively, such units only operate above ambient temperatures.
Accelerated fade units also require complex mechanical systems to ensure all the light sensitive materials are subject to the same, total amount of incident radiation no matter where they are located on a sample plane.
Such systems cause difficulty in testing the accelerated aging of light sensitive materials where the predominant source of aging will be due to incident light radiation, as the results are confounded by the use of elevated temperatures during the aging tests.
Alternatively, these systems can operate at reduced light levels to maintain the ambient temperature conditions. This removes the difficulty of interpreting the accelerated aging data, but it requires a longer period of time to perform the test procedures due to the use of lower light levels.
U.S. Pat. No. 4,760,748, issued to Kataynagi, et al, on Aug. 2, 1988, discloses an accelerated fade system based on a central light source, whereby a sample plane carrying light sensitive material rotates around a central light source. Thermal deterioration of the light sensitive material is inhibited by a cold air guide which encloses a portion of the rotating sample plane. The Kataynagi et al structure permits a large amount of light sensitive material to be loaded on the sample plane at one time, but requires a rotating sample assembly and an auxiliary cooling system.
U.S. Pat. No. 5,206,518, issued to Fedor, et al., on Apr. 27, 1993, discloses an accelerated fade unit based on a bank of lamps having an appropriate barrier array with a multiple detector feedback system to achieve a uniform power distribution over the sample plane. The Fedor et al structure permits a large amount of sample material to be loaded on the sample plane at one time, and it does not require any movement of the sample plane to maintain uniformity of light exposure at the sample plane. Fedor et al suffer from certain limitations. They require multiple lamps to obtain spatial uniformity of the incident light. They also require a complex system of detectors and feedback circuitry to control the lamp outputs individually. Finally, they use cooling air at the sample plane for temperature control.
Commonly assigned U.S. Pat. No 5,734,115, issued to Camp, et. al. on Jun. 16, 1998, employ an integrating sphere to allow the light sensitive material to remain stationary during the test. Camp et. al. suffer from certain design limitations in that the amount of light sensitive material that can be accommodated by the accelerated fade unit is limited to approximately 20 square inches of material at one time.
Commonly-assigned U.S. Pat. No. 5,767,423, issued to Camp, et. al., on Dec. 4, 1996 discloses a cooled sample holder for use in an accelerated fade apparatus that eliminates the need for external air cooling. Camp et. al. suffers from certain limitations. The disclosed holders are only capable of handling several square inches of light sensitive materials at any one time.
It is an object of the present invention to provide improved apparatus for the accelerated aging of light sensitive materials at high levels of incident radiation without suffering substantial heat problems.
It is a further object of the present invention to create high levels of incident radiation at only slightly elevated ambient temperatures.
It is another object of the present invention to operate at slightly elevated temperature without requiring additional cooling capabilities.
It is yet a further object of the present invention to permit for a large sample plane without requiring any complex mechanical subsystems.
A still further object of the present invention is to provide a uniform and stable source of incident radiation.
It is a further object of the present invention to provide for easy addition and removal of light sensitive materials from the apparatus.
These objects are achieved in an apparatus for subjecting light sensitive materials to visible radiation while minimizing the amount of heat generated, comprising:
(a) a source of visible radiation including at least one microwave energy responsive sulfur bulb;
(b) means for applying microwave energy to the microwave energy responsive sulfur bulb to cause such microwave energy responsive sulfur bulb to emit visible light;
(c) a holder defining a surface for receiving light sensitive materials located relative to the microwave energy responsive sulfur bulb; and
(d) a light diffusing assembly disposed relative to the microwave energy responsive sulfur bulb and responsive to the visible light emitted by the microwave energy responsive sulfur bulb to illuminate light sensitive materials received by the holder with diffused uniform visible light.
A microwave energy responsive sulfur bulb provides a stable visible light source which does not produce excessive quantities of heat.
It is a feature of the present invention that microwave energy responsive sulfur bulbs are commercially available.